As a mother screams on the delivery table, her newborn suddenly pops out and cuts the umbilical cord after googling how to do it on his father's tablet. The baby then grabs the nurse's phone and Instagrams a selfie, crawls to a laptop on the floor and signs into multiple social networking sites, and uses a GPS to find his way out of the hospital.

This recent "Born for the Internet" ad campaign by mobile service provider MTS for its 3G Plus network is a bit extreme, but it's not uncommon these days to see babies and toddlers swiping away on their parents' touch screen gadgets.

Screen time crowds out other activities that kids should be engaging in

matthew davis, university of michigan

Evidence from an increasing number of research studies suggests that limiting a child's screen time is the best approach. Screen time includes watching television and using the internet and other electronic devices such as mobile phones, tablets and video games.

Children get more sleep, do better in school, behave better and see other health benefits when parents limit content and the amount of time their children spend on the computer or in front of the TV, according to a study by Iowa State University published in March in JAMA Pediatrics.

At an American College of Cardiology conference in March, University of Michigan researchers presented findings from a study of more than 1,000 sixth graders from 24 middle schools in southeast Michigan. They found that children who had more screen time snacked more often and were more likely to choose less healthy snacks.

Many studies have established positive correlations between excessive TV and video game use and weight gain among children. But the effects aren't just physical - children who spend most of their time on electronic devices tend to be more insular and lacking in communication skills.

"Modern electronic devices like smartphones, computers and tablets are useful resources to get children engaged in learning language, but they cannot be the only medium of acquiring language," says speech-language pathologist Arthur Fang.

The first two years are the most crucial in a child's development. Early childhood is critical for brain development and formation of behaviour. Between two and four, even incremental television exposure can delay development.

Last year, the American Academy of Pediatrics updated its recommendations for children's screen time: for those under two years of age, it discourages any screen time. For older children, no more than two hours daily. Further, it suggests keeping media devices out of children's bedrooms, keeping family routines like mealtimes screen-free, and setting screen-free days for the whole family.

The Hong Kong Health Department adopts similar recommendations. Parents should encourage children to participate in physical activities and offer them various options to develop their skills.

"When you get to three or four hours each day, that screen time crowds out other important activities that babies and young kids should be engaging in: looking at books, going for walks or playing outside," says Dr Matthew Davis, a professor of health management and policy at the University of Michigan.

In a poll taken in March that involved 560 parents of children under the age of five, the Michigan researchers found that about a quarter of parents said their children got three or more hours of screen time a day.

Prolonged screen time also leads to short-sightedness (myopia), already a prevalent problem in children. In a two-year study by Polytechnic University and the Hong Kong Paediatric Foundation that involved more than 5,000 schoolchildren aged between five and 19, it was found that about 70 per cent did not maintain the correct minimum distance from the eyes to the screen when using digital electronic gadgets or computer screens.

The recommended distance is at least 50cm from notebooks and computers, at least 40cm for tablets or ebook readers, and at least 30cm for smartphones.

How can parents limit their children's screen time? The key solution is for them to be good role models themselves. The amount of time they spend in front of a screen is closely associated with their parents' own habits, say University of Bristol researchers.

In a study published in the International Journal of Behavioural Nutrition and Physical Activity, they found that children were 3.4 times more likely to spend more than two hours a day watching television if their parents did the same, compared with children whose parents watched less TV.

Among the five- and six-year-old children from 1,078 families, 12 per cent of boys and 8 per cent of girls watched more than two hours of television on a weekday, with 30 per cent of parents exceeding this threshold.

Figures were much higher at weekends, with 45 per cent of boys, 42 per cent of girls, 57 per cent of fathers and 53 per cent of mothers watching more than two hours of television each day.

"The results highlight that any guidance related to excessive screen viewing should involve both parents and children," says Dr Sanjay Thakrar, research adviser at the British Heart Foundation.

Another good approach to limiting screen time is through location rather than counting minutes. "It's easier to say no smartphones at the table, than watch the clock," says Davis.

Dr Theodote Pontikes, paediatric psychiatrist at Loyola University Health System in Illinois, suggests parents discuss with their children and set limits together. At the same time they need to help them understand why limits are needed.

"You don't need to follow your child on Twitter or friend them on Facebook, but make sure you're communicating face-to-face," says Pontikes.

"A relationship has to be about more than social media. Make sure you are having intentional face-to-face time with your kids and encourage them to have more personal interactions with their friends."